Method and system for determining a number of transfer objects which move within an observed region

ABSTRACT

The invention proposes a method for determining a number ( 13 ) of transfer objects which are moving from a first subregion ( 8 ) of an observed region ( 5 ) into a second subregion ( 9 ) of the observed region ( 5 ), wherein a succession of images of the observed region ( 5 ) is recorded which identify objects ( 1; 2; 3; 4 ) and determine positions ( 1   b   , 1   c   ; 2   a   , 2   b   , 2   c   ; 3   a   , 3   b   , 3   c   ; 4   a   , 4   b ) for the objects ( 1; 2; 3; 4 ), respectively, the objects ( 1; 2; 3; 4 ) are each associated either with the first subregion ( 8 ) or with the second subregion ( 9 ) on the basis of the positions ( 1   b   , 1   c   ; 2   a   , 2   b   , 2   c   ; 3   a   , 3   b   , 3   c   ; 4   a   , 4   b ) of said objects, and multiple transfers of the same object between the first subregion ( 8 ) and the second subregion ( 9 ) are taken into account when determining the number ( 13 ) of transfer objects. The invention likewise proposes an appropriate system which can be used to carry out the method, said system comprising a sensor arrangement and a computation unit connected to the sensor arrangement.

BACKGROUND

The invention relates to a method and a system for determining a numberof transfer objects which move from a first sub-region of an observedregion into a second sub-region of the observed region.

In many fields of technology and daily life, great importance isattached to the counting of movable objects. For example, a storeowneris interested to know how many visitors visit his store within a givenperiod of time.

In the counting methods known from the prior art for applications ofthis type and similar applications, systems that comprise a video cameraconnected to an image analysis unit are used as a counting device. Asystem of this type is designed to observe a region, for example theentry region of a shop or means of transport, to recognise and localiseobjects moving in the region, and to trigger a counting event when oneof the objects crosses a predefined boundary running in the region, forexample a door threshold, which runs in the region and divides it.

These known methods have the disadvantage however that objects whichmove to and fro within the observed region and pass the boundary anumber of times in so doing trigger a counting event each time they passthe boundary. Objects that display such behaviour are also referred toas re-entrants. These can falsify a result of the count considerably.

SUMMARY OF THE INVENTION

The object of the present invention is therefore to develop a method anda system with the aid of which movable objects can be counted asreliably as possible no matter how the objects move.

A method for determining a number of transfer objects which move from afirst sub-region of an observed region into a second sub-region of theobserved region is described, wherein

-   -   a sequence of images of the observed region is recorded, in        which objects are identified and positions of the objects are        determined,    -   the objects, depending on their positions, are associated with        either the first or the second sub-region, and    -   multiple transfers of the same object between the first        sub-region and the second sub-region are taken into account when        determining the number of transfer objects.

With the aid of this method, it is possible to reliably determine thenumber of transfer objects. Since multiple transfers of the same objectbetween the first sub-region and the second sub-region are taken intoaccount when determining the number of transfer objects, errors such asthose that occur with counting methods according to the prior art whenre-entrants are counted a number of times can be corrected effectively.

The sequence of images of the observed region can be recorded using asensor arrangement that preferably comprises an optical sensor. Theoptical sensor can be formed as a simple photo camera, as a CCD camera,as a stereo camera, as a video camera, as a streak camera or as atime-of-flight camera. The recording is characterised by an exposuretime and by an image repetition rate. Here, the image repetition rateindicates how many images are recorded in a given period of time. Whenrecording images using a sensor arrangement, the observed region is theregion that is observed by the sensor arrangement. Typically, theobserved region is three-dimensional and contiguous. The firstsub-region and the second sub-region of the observed region arepreferably selected in such a way that the observed region is a disjunctcombination of the first sub-region and the second sub-region. Here, thefirst sub-region and the second sub-region may also be contiguous. Thefirst sub-region and the second sub-region are separated by a boundary.In a period of observation, which is given by the recording of thesequence of images, the objects move in the observed region. A number ofobjects identified in the images may be subject to changes. Objects mayconstantly leave the observed region and re-enter it. The exposure timeand the image repetition rate are preferably adapted to the speeds atwhich the objects move in the observed region. To this end, the exposuretime may be selected in such a way that a first path covered by anobject within the exposure time is less than a first threshold value.The image repetition rate can also be selected in such a way that asecond path covered by an object between the recording of two successiveimages is less than a second threshold value.

A transfer of an object between the first sub-region and the secondsub-region is either a transfer of the object from the first sub-regioninto the second sub-region or a transfer of the object from the secondsub-region into the first sub-region. Between the recording of a firstimage and a second image, a transfer of an object from the firstsub-region into the second sub-region has taken place if the object isassociated in the first image with the first sub-region and if theobject is associated in the second image with the second sub-region. Atransfer of an object from the second sub-region into the firstsub-region is defined in a similar manner. A multiple transfer of thesame object is then present if this object moves in the sequence ofimages at least once from the first sub-region into the secondsub-region and back again from the second sub-region into the firstsub-region. A multiple transfer of the same object is then also presentif this object moves in the sequence of images at least once from thesecond sub-region into the first sub-region and back again from thefirst sub-region into the second sub-region. A multiple transfer of thesame object is thus then present if this object passes the boundarybetween the first and the second sub-region at least twice. Theconsideration of the number of transfer objects comprises at least onecheck of the number. This may, but does not have to, involve a change ofthe number.

Within the meaning of the present invention, transfer objects arefirstly objects that are associated in a first of the sequence of imageswith the first sub-region and which, at the end of the sequence ofimages or immediately before they leave the observed region, areassociated with the second sub-region. Within the meaning of the presentinvention, transfer objects are additionally also objects which, in thesequence of images, enter the observed region from outside the observedregion and which, in the observed region, are at first associated withthe first sub-region and which, at the end of the sequence of images orimmediately before they leave the observed region, are associated withthe second sub-region. All other objects are not transfer objects withinthe meaning of the present invention. In other words, with the methodand system described here, counting is only implemented in onedirection—from the first sub-region into the second sub-region. Countingin an opposite direction—from the second sub-region into the firstsub-region—can be easily carried out similarly to the counting methoddescribed here by swapping the first and the second sub-region. Thesystem and method described here can thus also be used for simultaneouscounting in both directions.

In an advantageous embodiment of the invention, the identification ofthe objects in the images comprises a segmentation of the images. Thesegmentation comprises a combining of individual image pixels of theimages to form segments. Segmentation can be performed on the basis ofgrey-scale values of the image pixels. A segment preferably correspondsto an identified object. The position of an identified object can beselected for example as a centre point of a segment. An image backgroundcan be taken into account during the segmentation process.

In a further advantageous embodiment of the invention, a track isassociated with each of the objects and is determined from positions ofthe object in the sequence of images, wherein the track has a startingposition located either in the first or in the second sub-region. Thetrack thus comprises positions of the same object in successive images.A track may also comprise just one single current position of theobject. Two positions determined in successive images are thenpreferably associated with the same track if they are adjacent. Thismeans that a spacing between the two positions is smaller than a maximumspacing. With regard to the association, a multiplicity of more than twosuccessive positions can also be taken into account however. Themovement of an object in the sequence of images can thus be followedreliably.

The track of an object then ends when the object leaves the observedregion. The starting position may be the position of an object that isidentified for the first time after an entry into the observed region.The starting position can also be the position of an object identifiedin a first image. The starting position can also be the position of anobject that has left the observed region in the meantime and has thenre-entered the observed region. When the object leaves the observedregion, the track can be either deleted or can remain stored. Since atrack is associated with each of the objects, it is possible to followthe movement of the objects in the sequence of images.

In a further advantageous embodiment of the invention, a memory state isassociated with each of the objects on the basis of its track and, witha given starting position of the track, is dependent on whether therespective object is associated with the first or the second sub-region.The memory state is preferably initialised with a predefined value whenthe respective object is identified for the first time. The memory stateof an object comprises additional information concerning the movementthereof in the observed region. The memory state of an object preferablyremains stored when this object leaves the observed region.

In a further advantageous embodiment of the invention, the determinationof the number of transfer objects comprises an updating of the numberafter a transfer of one of the objects between the first and the secondsub-region, wherein the update is performed in accordance with thememory state of the respective object and in accordance with a directionof the transfer of the respective object. Here, the update may comprisethe fact that the number of transfer objects is incremented, that thenumber of transfer objects is decremented, or that the number oftransfer objects is not changed. The number of transfer objects when therecording of the sequence of images is begun is preferably initialisedwith a starting value. Here, the direction of the transfer of therespective object denotes whether the respective object has transferredfrom the first sub-region into the second sub-region or whether therespective object has transferred from the second sub-region into thefirst sub-region. The current memory state is preferably alwaysestablished before the number of transfer objects is updated. The numberof transfer objects is thus updated once one or more of the objectshas/have passed the boundary between the first sub-region and the secondsub-region. The execution of the updating process in accordance with thememory state and the direction of the transfer of the respective objectmakes it possible to identify the presence of a multiple transfer ofsaid object.

In a further advantageous embodiment of the invention, the memory stateis a first memory state when the starting position of the track of therespective object and the current position of the respective object areeach located in different sub-regions, and the memory state is a secondmemory state when the starting position of the respective object and thecurrent position of the respective object are located in the samesub-region. The memory state of an object therefore changes when theobject passes the boundary between the first sub-region and the secondsub-region. The memory state of an object does not change provided theobject remains in the same sub-region.

In a further advantageous embodiment of the invention, the memory stateis a number that is incremented by a first value each time therespective object transfers between the first and the second sub-region,wherein the first memory state is present when the number is an oddmultiple of the first value, and wherein the second memory state ispresent when the number is an even multiple of the first value. From thememory state of an object, it is thus possible to establish how oftenthe respective object has crossed the boundary between the first and thesecond sub-region. It is advantageous if the number in the event of afirst identification of the respective object is initialised with astarting value. It is expedient to select 0 as a starting value. If, inthis case, the first value is set equal to 1, the memory state of therespective object thus immediately indicates how often the respectiveobject has passed the boundary between the first and the secondsub-region.

In a further advantageous embodiment of the invention, the number oftransfer objects is updated in such a way that the number of transferobjects is incremented by a second value when the respective objecttransfers from the first into the second sub-region and the memory stateof the respective object is the first memory state, and in such a waythat the number of transfer objects is decremented by the second valuewhen the respective object transfers from the second into the firstsub-region and the memory state of the respective object is the secondmemory state. In this case too, the memory state of the respectiveobject is advantageously established first, and only then is the numberof transfer objects updated.

It is particularly advantageous if an increment variable and a decrementvariable are associated with each identified object and are stored. Theincrement variable is incremented by the second value when the number oftransfer objects is incremented by the second value after a transfer ofthe respective object. Similarly, the decrement variable is decrementedby the second value when the number of transfer objects is decrementedby the second value after a transfer of the respective object. Thevalues of the increment variable and of the decrement variable of therespective object also then preferably remain stored when the objectleaves the observed region. In this way, a number of re-entrants can bedocumented and understood. This may be of practical significance, forexample when the observed region is an entry and exit region ofsuccessive escalators, as can be found typically in department stores.In this case, the first region may be a path covered by escalators, saidpath comprising a first escalator between a first and a second level anda second escalator between the second and a third level, and the secondregion may be part of the second level of the store. A person who,coming from the first escalator, that is to say from the firstsub-region, briefly enters the second level, that is to say the secondsub-region, and then steps onto the second escalator and thereforere-enters the first sub-region does not contribute on the whole to achange of the number of transfer objects—in the example these arevisitors to the second level. The increment variable and the decrementvariable are designed such that this short visit to the second levelremains documented however.

In a further specific embodiment, an object, preferably each object,that transfers or is transferred at least once from the first sub-regioninto the second sub-region or that transfers or is transferred at leastonce from the second sub-region into the first sub-region is marked asan entrant and/or as a leaver, wherein the object

-   -   is marked as an entrant if its starting position is located in        the first sub-region,    -   is marked as a leaver if its starting position is located in the        second sub-region, and    -   is marked both as an entrant and as a leaver if the memory state        of the object is the second memory state.

The marking may comprise an association of an entrant attribute and/or aleaver attribute. For example, an entrant variable and/or a leavervariable, which may each adopt precisely two different values, that isto say a starting value and an end value, can be associated with eachidentified object. Here, the starting value may be zero and the endvalue may be one. However, non-numerical values are also conceivable.The entrant variable and the leaver variable are preferably eachinitialised with the starting value when the object is identified forthe first time. If the entrant variable is set to the starting value,the corresponding object is therefore not marked as an entrant. Equally,the object is not marked as a leaver if the leaver variable of theobject is set to the starting value. By setting the entrant variable tothe end value, the corresponding object can be marked as an entrant.Similarly, the object can be marked as a leaver by setting the leavervariable to the end value. The values of the entrant variable and of theleaver variable preferably remain stored when the object leaves theobserved region. Other embodiments of the marking process are alsoconceivable. It is key that the marking process is performed orimplemented in such a way that it is possible to determine at any momentfor an identified object, preferably for each identified object, whetheror not this object is marked as an entrant and/or whether or not thisobject is marked as a leaver. The marking of an object is preferablychecked immediately after each transfer of the object between thesub-regions and is updated where appropriate.

By counting the objects marked in this way as entrants and/or asleavers, an entrant number and/or a leaver number can preferably bedetermined at any moment, wherein the entrant number is then equal tothe number of objects marked as entrants, and/or wherein the leavernumber is then equal to the number of objects marked as leavers. Furtherinformation concerning the objects that remains unconsidered in thepreviously described embodiments can thus be obtained. For example, thedetermination of the entrant number and/or of the leaver number can beused when counting customers in a department store in which a salesstand is located in the door region, wherein the door threshold is to bethe boundary between the first and the second sub-region, and whereinthe stand is to be located in the second sub-region. It is conceivablein this case for a customer coming from outside to cross the doorthreshold, that is to say to move from the first sub-region via theboundary into the second sub-region, to speak with an advisor at thesales stand and to then move back into the first sub-region and leavethe department store. This customer is identified as a re-entrant andconsequently is not counted as a transfer object. When counting theobjects marked as entrants and/or as leavers, this customer is takeninto account however.

A system for determining a number of transfer objects which move from afirst sub-region of an observed region into a second sub-region of theobserved region comprises at least one sensor arrangement and acomputation unit connected to the sensor arrangement, wherein the sensorarrangement is designed to record a sequence of images of the observedregion, and wherein the computation unit is programmed.

-   -   to identify objects in the images and to determine positions of        the objects,    -   to associate each of the objects, in accordance with their        positions, either with the first or the second sub-region, and    -   to take into account multiple transfers of the same object        between the first sub-region and the second sub-region when        determining the number of transfer objects.

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments of the invention are illustrated in the followingdrawings and will be explained in greater detail in the followingdescription. In the drawings

FIG. 1 shows a schematic view of an entry region of a building, in whichpeople are moving, observed by a sensor arrangement,

FIG. 2 shows a schematic view of a first recording of the entry regionfrom FIG. 1, wherein the recording has already been subject tosegmentation,

FIG. 3 shows the first recording, wherein, after segmentation, positionsof some individuals from FIG. 1 have been determined,

FIG. 4 shows a schematic view of a second recording of the entry regionwith positions and tracks of identified individuals,

FIG. 5 shows a schematic view of a fourth recording of the entry region,likewise with positions and tracks of identified individuals, and

FIG. 6 shows a schematic view of a track of an individual in the entryregion via a sequence of five recordings, wherein the individual is ineach case marked as an entrant and/or as a leaver.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a schematic view of an entry region of a building, whichfor example is a department store. A sensor arrangement 14 can be seenand is designed to observe the entry region. In the present exemplaryembodiment, the sensor arrangement 14 is formed as an individual videocamera. A photo camera, a stereo camera, a streak camera or atime-of-flight camera can also be used as a sensor arrangement 14. Thesensor arrangement 14 may also comprise a combination of a plurality ofidentical or different sensors. These are preferably optical sensorshere. A computation unit which is arranged in the sensor arrangement 14and is connected to the sensor arrangement 14 cannot be seen.Individuals, that is to say the objects 1, 2, 3 and 4, move in the entryregion. The sensor arrangement 14 is designed to record a sequence ofimages of the entry region. The objects 1, 2, 3 and 4 move in the entryregion typically at a speed of approximately 1 m/s. An exposure time andan image recording rate of the sensor arrangement 14 are adapted to thisspeed. The image recording rate of the sensor arrangement 14 is thusapproximately 20 Hz, and the exposure time of an individual image of thesequence of images is 40 ms.

FIG. 2 shows a first of the sequence of images, which illustrates anobserved region 5. The observed region 5 has a rectangular shape with alength 6 of approximately 5 m and a width 7 of approximately 3 m. Aboundary 10 runs through the observed region and divides it into a firstsub-region 8 and a second sub-region 9. The boundary 10 for examplereproduces the course of a door threshold in the entry region. In thefirst image shown in FIG. 2, which is also to be called a firstrecording, the image recorded by the sensor arrangement 14 has alreadybeen segmented. Segments 2′, 3′ and 4′ obtained from the segmentationare illustrated. The segments 2′, 3′ and 4′ correspond to the objects 2,3 and 4 respectively, shown in FIG. 1. By means of this segmentation,the objects 2, 3 and 4 in the observed region 5 have each beenidentified. The object 1 shown in FIG. 1 is located outside the observedregion 5 and has therefore not been identified in FIG. 2. Recurringfeatures are provided with the same reference signs in the followingfigures.

FIG. 3 again shows the first recording of the sequence of imagesillustrated already in FIG. 2, wherein the computation unit hasdetermined from the segments 2′, 3′ and 4′, with the aid of which theobjects 2, 3 and 4 have been identified, positions 2 a, 3 a and 4 a ofthe objects 2, 3 and 4. An identification of objects by means ofsegmentation and a subsequent determination of positions of therespective objects from the segments are achieved in a similar manner ineach of the sequence of images, these processes being carried out ineach case by the computation unit. In each of FIGS. 3 to 5, onlypositions of objects are shown. These are in each case representativefor the objects associated with the positions.

The computation unit is designed to associate the objects 2, 3 and 4, ineach case in accordance with their respective positions 2 a, 3 a and 4a, either with the first sub-region 8 or the second sub-region 9. Theobjects 3 a and 4 a are thus associated with the first sub-region 8 inFIG. 3. The object 2 a is associated with the second sub-region 9.Hereinafter, a determination of a number of transfer objects which movefrom the first sub-region 8 of the observed region 5 into the secondsub-region 9 of the observed region 5 will be described.

In FIG. 3, a track is associated with each of the objects associatedwith the positions 2 a, 3 a and 4 a and is determined from positions ofthe respective object in the sequence of images. In the first imageillustrated in FIG. 3, the tracks of the objects 2, 3 and 4 areidentical to the positions 2 a, 3 a and 4 a respectively. In the firstimage shown in FIG. 3, each of the tracks thus comprises just oneposition. Here, each of the positions 2 a, 3 a and 4 a in FIG. 3 is alsoa starting position of the respective track.

In FIG. 3, a number 21, which is initialised with 0, is additionallyassociated with the object 2 having the position 2 a. Accordingly,numbers 31 and 41, which are likewise each initialised with 0, areassociated with the objects 3 and 4 having the positions 3 a and 4 arespectively. A value of the number 21 is intended to indicate how oftenthe corresponding object 2 has passed the boundary 10 between the firstsub-region 8 and the second sub-region 9. The numbers 31 and 41 withregard to the objects 3 and 4 have a similar meaning. The numbers 21, 31and 41 constitute a memory state of the objects 2, 3 and 4 respectively.A number 13 of the transfer objects is initialised with 0 in the firstrecording of the sequence of images illustrated in FIG. 3. This meansthat none of the identified objects 2, 3 and 4 has yet been recognisedas a transfer object in the first recording.

FIG. 4 shows a second image of the sequence of images, which will alsobe referred to as a second recording and has been recordedchronologically after the first image shown in FIG. 3. In the secondrecording, segmentation has already been carried out and currentpositions 1 b, 2 b, 3 b and 4 b of the objects 1, 2, 3 and 4 havealready been determined, wherein the current positions are eachillustrated as black dots. Between the first recording shown in FIG. 3and the second recording shown in FIG. 4, the object 2 has moved fromthe position 2 a, which is located in the second sub-region 9, to thecurrent position 2 b, which is located in the first sub-region 8. Atrack 22, which comprises the position 2 a of the object 2 as a startingposition and also the current position 2 b of the object 2, isassociated in FIG. 4 with the object 2 having the position 2 b.

Between the first and the second recording, the object 2 has transferredfrom the second sub-region 9 into the first sub-region 8. After thistransfer of the object 2, the number 21 associated with the object 2,this number representing the memory state of the object 2, isincremented by a first value. Here, the first value is equal to 1. InFIG. 4, the value of the number 21 associated with the object 2 istherefore 1. The memory state of the object 2 in FIG. 4 is therefore afirst memory state, which is characterised in that the number 21 is anodd multiple of the first value 1. In other words, p mod 2=1 is true forthe number 21 in the first memory state, wherein “p” assumes the valueof the number in the first memory state, and wherein “mod” is the modulooperator. The first memory state of the object 2 in FIG. 4 is alsocharacterised in that the current position 2 b of the object 2 and thestarting position 2 a of the track 22 of the object 2 are each locatedin different sub-regions. In other words, the first memory state is thenpresent if the respective object has passed the boundary 10 an oddnumber of times.

Once the object 2 has passed the boundary 10 and the number 21associated therewith has been incremented by 1, the number 13 oftransfer objects is updated, specifically in accordance with the memorystate of the object 2 and in accordance with a direction in which theobject 2 has passed the boundary 10. In the case of the object 2, whichin FIG. 4 is in the first memory state and has passed the boundary 10 inthe direction from the second sub-region into the first sub-region, theupdate includes the fact that the number 13 is not changed.

The object 1, with which the current position 1 b is associated in FIG.4, was identified for the first time in FIG. 4. A track can also beassociated with this object, said track comprising just the currentposition 1 b itself however. A number 12, which is initialised with 0and is a memory state of the object 1, is additionally associated withthe object 1.

In FIG. 4, the current position 3 b is associated with the object 3. Atrack 32 is additionally associated with the object 3 and comprises thecurrent position 3 b and a starting position 3 a, wherein the latter isidentical to the position 3 a of the object 3 determined in the firstrecording. The number 31 associated with the object 3 is incremented by1 once the object 3 has passed the boundary 10 and thus has the value 1in FIG. 4.

In FIG. 4, the object 3 has transferred from the first sub-region 8 intothe second sub-region 9. The number 31 associated with object 3 has thevalue 1 in FIG. 4 and thus represents a first memory state of the object3. As a result of this transfer of the object 3 between the first andthe second recording, the number 13 of transfer objects is thereforeincremented by 1, wherein 1 is a second value. In FIG. 4, a situation ofthe object 4, with which a track 41 is likewise associated, is similarto the situation of the object 3. As a result of the transfer of theobject 4 from the first sub-region 8 into the second sub-region 9, thenumber 13 of the transfer objects is therefore also incremented by 1.Once the number 13 of transfer objects has been updated for the objects2, 3 and 4 which have been identified in FIG. 4 and which have eachcrossed the boundary 10 between the first and the second recording, thenumber 13 of transfer objects in FIG. 4 has the value 2. This isequivalent to the fact that, in the course of the first and the secondrecording, two objects, specifically the object 3 and the object 4,which were each identified at first in the first sub-region 8, havecrossed over from the first sub-region 8 into the second sub-region 9.

FIG. 5 shows a third recording of the sequence of images. The objects 1,2 and 3 have been identified by segmentation and the positions 1 c, 2 cand 3 c thereof respectively have been determined. The object 2 hasmoved between the second and the third recording from the position 2 bin the first sub-region 8 into the position 2 c in the second sub-region9. The track 22 associated with the object 2 therefore comprises thecurrent position 2 c of the object 2 and also the position 2 bdetermined in the second recording and the position 2 a determined inthe first recording, which is a starting position of the track 22. Theobject 2 has thus crossed the boundary 10 again. The number 21associated with the object 2 is therefore again incremented by 1 and nowhas the value 2 in FIG. 5. The number 21 therefore represents a secondmemory state of the object. This is characterised on the one hand inthat the current position 2 c of the object 2 and the starting position2 a of the track 22 of the object 2 are associated with the samesub-region, specifically the second sub-region 9 here. On the otherhand, the second memory state of the object 2 is defined in that thenumber 21 has a value which is an even multiple of the first value. (Thefirst value has the value 1 and the number 21 in FIG. 5 has the value2). In other words, q mod 2=0 is true for the number 21 in the secondmemory state, wherein “q” assumes the value of the number in the secondmemory state, and wherein “mod” is the modulo operator, as before.

After the transfer of the object 2, the number 13 of transfer objects isupdated. In the case of object 2 in FIG. 5, the update does not includea change to the number 13 however. The current position 2 c and thestarting position 2 a of the track 22 of the object 2 are both locatedin the second sub-region 9. The object 2 in FIG. 5 is therefore are-entrant and does not contribute to the number 13 of transfer objects.There is thus a multiple transfer of said object, specifically theobject 2, between the first sub-region 8 and the second sub-region 9.

The object 1 has moved between the second recording and the thirdrecording from the position 1 b into the current position 1 c. A track12 associated with the object 1 therefore comprises the positions 1 cand the position 1 b, wherein the position 1 b is a starting position ofthe track 12 of the object 1. The object 1 has not passed the boundary10 between the first sub-region 8 and the second sub-region 9 betweenthe second and the third recording. The number 11 associated with theobject 1 is therefore not incremented and furthermore has the value 0.In FIG. 5, the number 13 is not updated for the object 1.

The object 3 between the second and the third recording has in turnmoved from the position 3 b located in the second sub-region 9 into thecurrent position 3 c, which is located in the first sub-region 8. Theobject 3 has thus passed from the second sub-region 9 into the firstsub-region 8. As a result of this transfer of the object 3, the number31 associated with the object 3 has in turn been incremented by 1 andnow has the value 2. The memory state of the object 3 in FIG. 5 istherefore a second memory state. As a result of this transfer of theobject 3 from the second sub-region into the first sub-region, thenumber 13 of transfer objects is therefore decremented by 1 and now hasthe value 1. Here, 1 is again the second value.

The object 4 has left the observed region 5 in FIG. 5 and is notidentified. The object 4 in FIG. 5 therefore does not contribute to theupdating of the number 13 of transfer objects. Once the number 13 oftransfer objects in FIG. 5 has been updated for all objects identifiedin FIG. 5, the number 13 of transfer objects has the current value 1. Itis clear from the track 22 of the object 2 and from the track 32 of theobject 3 that the objects 2 and 3 are each re-entrants. In FIG. 5, theobject 2 and the object 3 have therefore each transferred twice via theboundary 10 between the first sub-region 8 and the second sub-region 9.The objects 2 and 3 in FIG. 5 are therefore each multiple transfers ofsaid objects, which have each been recognised. With the provisionsdescribed here for determining the number 13, multiple transfers of thistype of the same object between the first sub-region 8 and the secondsub-region 9 are taken into account.

FIG. 6 shows a track of an object over a sequence of five images.Positions 50 a-50 e of the object in the individual images, by means ofwhich the track is determined, are each indicated as circles. Recurringfeatures are provided with identical reference signs, as before. In theexemplary embodiment described here, besides a memory state, which isgiven in the sequence of images by values 51 a-51 e and which representsthe number of transfers of the object between the first sub-region 8 andthe second sub-region 9 already carried out by the object in therespective image, an entrant variable and a leaver variable areadditionally associated with the object. The entrant variable assumesvalues 52 a-52 e in the sequence of images. The values 52 a-52 e of theentrant variable here have the value 0 when the object is not marked inthe respective image as an entrant, and the value 1 when the object ismarked in the respective image as an entrant. Accordingly, the leavervariable in the sequence of images assumes values 53 a-53 e. The values53 a-53 e of the leaver variable have the value 0 when the object in therespective image is not marked as a leaver, and the value 1 when theobject in the respective image is marked as a leaver. The number oftransfer objects is determined in the exemplary embodiment shown here asdescribed before and is therefore not explained in greater detail.

In the first of the sequence of images, in which the object isindentified for the first time and adopts the starting position 50 a inthe first sub-region 8 of the observed region 5, the value 51 a of thememory state, the value 52 a of the entrant variable, and the value 53of the leaver variable are each initialised with the value 0. Theobject, which has not yet passed the boundary 10 in the first image, istherefore marked in the first image neither as an entrant nor as aleaver. An entrant number not specified separately here, which is equalto a number of objects marked as entrants, is therefore likewise 0 inthe first image. A leaver number, which is not specified separately hereand is equal to a number of objects marked as leavers, is also 0 in thefirst image. Since, in the sequence of images in FIG. 6, only one objectis in each case identified and marked as an entrant and/or as a leaver,the entrant number in the sequence of images is equal to the respectivevalue of the entrant variable, and the leaver number is equal to therespective value of the leaver variable. The updating of the entrantnumber and the leaver number will therefore not be discussed in greaterdetail hereinafter. From image to image, the object moves to and frobetween the first sub-region 8 and the second sub-region 9 via theboundary 10. The number of transfer objects, not shown here, is also 0in the first image.

In the second image, the second position 50 b of the object is locatedin the second sub-region 9. The value 51 b of the memory state isincremented by 1 and now has the value 1. Since the value 51 b of thememory state in the second image is even, the memory state of the objectin the second image is a first memory state. Once the memory state hasbeen updated, the values 52 b of the entrant variable and 53 b of theleaver variable are updated. Since the starting position of the objectis located in the first sub-region 8 and the object has already passedthe boundary 10 once in the second image, as can be deduced from thevalue 51 b of the memory state, the value 52 b of the entrant variableis set to 1. The object is therefore marked as an entrant. Since neitherthe starting position 50 a is located in the second sub-region nor isthe memory state of the object a second memory state, the value 53 b ofthe leaver variable in the second image is still 0. The object istherefore not marked as a leaver in the second image. The number oftransfer objects is 1 in the second image and is therefore equal to theentrant number.

In the third image, the third position 50 c of the object is againlocated in the first sub-region 8. The object has thus again passed theboundary 10 between the second and the third image. The value 51 c ofthe memory state is therefore incremented by 1 and now has the value 2.Since the value 51 c is even, the memory state of the object in thethird image is the second memory state. Once the memory state has beenupdated, the value 52 c of the entrant variable and the value 53 c ofthe leaver variable are updated. Since the object has passed theboundary 10 at least once, specifically exactly twice, in the thirdimage and the memory state is the second memory state, the value 52 c ofthe entrant variable and the value 53 c of the leaver variable areeach 1. The object is thus marked in the third image both as an entrantand as a leaver. Since the object in the third image is a re-entrant,the number of transfer objects in the third image is 0 and is thereforedifferent from the entrant number, which is 1.

The fourth position 50 d in the fourth image is again located in thesecond sub-region 9. The object has therefore passed the boundary 10again between the third and the fourth image. The value 51 d of thememory state is increased by 1 to 3, such that the memory state in thefourth image is the first memory state. The value 52 d of the entrantvariable is still 1 in the fourth image, and the value 53 d of theleaver variable is again set to 0 in the fourth image. In the fourthimage, the number of transfer objects is again 1 and is therefore equalto the entrant number.

The fifth position 50 e in the fifth image is located in the firstsub-region 8. The object has therefore again passed the boundary 10between the fourth and fifth image. The value 51 e of the memory stateis increased by 1 to 4, and therefore the memory state in the fifthimage is the second memory state. The value 52 e of the entrant variableis still 1 in the fifth image, and the value 53 e of the leaver variableis again set to 1 in the fifth image since the object has passed theboundary at least once, specifically exactly four times, in the fifthimage and the memory state is the second memory state. In the fifthimage, the object is again a re-entrant. The number of transfer objectsis therefore again 0 and is different from the entrant number, which isstill 1.

The invention claimed is:
 1. A method for determining a number oftransfer objects which move from a first sub-region of an observedregion into a second sub-region of the observed region, comprisingrecording, using at least one sensor arrangement, a sequence of imagesof the observed region, and using a computation unit connected to the atleast one sensor arrangement and programmed to conduct the steps ofidentifying objects in the images, determining positions of the objects,associating each of the objects, in accordance with their positions,either to the first sub-region or the second sub-region, associating atrack with each of the objects, wherein the track is determined frompositions of the object in the sequence of images, wherein the track hasa starting position located either in the first sub-region or in thesecond sub-region, associating a memory state with each of the objectson the basis of its track wherein, with a given starting position of thetrack, the memory state is dependent on whether the respective object isassociated with the first sub-region or the second sub-region, whereinthe memory state is a number that, when the respective object transfersbetween the first sub-region and the second sub-region, is incrementedby a first value, wherein a first memory state is present if the numberis an odd multiple of the first value, and wherein a second memory stateis present if the number is an even multiple of the first value, andtaking into account multiple transfers of the same object between thefirst sub-region and the second sub-region when determining the numberof transfer objects.
 2. The method according to claim 1, whereinidentifying the objects in the images in each case comprises asegmentation of the images.
 3. The method according to claim 1, whereinthe determination of the number of transfer objects comprises updatingthe number of transfer objects once the objects have transferred betweenthe first sub-region and the second sub-region, and wherein the updateis performed in accordance with the memory state of the respectiveobject and in accordance with a direction of the transfer of therespective object.
 4. The method according to claim 1, wherein thememory state is the first memory state when the starting position of thetrack of the respective object and the current position of therespective object are each located in different sub-regions, and in thatthe memory state is the second memory state when the starting positionof the respective object and the current position of the respectiveobject are located in the same sub-region.
 5. The method according toclaim 3, wherein the updating process comprises the fact that the numberof transfer objects is incremented by a second value when the respectiveobject transfers from the first sub-region into the second sub-regionand the memory state of the respective object is the first memory state,and in that the number of transfer objects is decremented by the secondvalue when the respective object transfers from the second sub-regioninto the first sub-region and the memory state of the respective objectis the second memory state.
 6. The method according to claim 4, whereinan object which passes at least once from the first sub-region into thesecond sub-region or which passes at least once from the secondsub-region into the first sub-region is marked as an entrant or as aleaver, wherein the object is marked as an entrant if its startingposition is located in the first sub-region, is marked as a leaver ifits starting position is located in the second sub-region, and is markedas an entrant and as a leaver if the memory state of the object is thesecond memory state.
 7. A system for determining a number of transferobjects which move from a first sub-region of an observed region into asecond sub-region of the observed region, said system comprising atleast one sensor arrangement and a computation unit connected to thesensor arrangement, wherein the sensor arrangement is designed to recorda sequence of images of the observed region, and wherein the computationunit is programmed to identify objects in the images and to determinepositions of the objects, to associate each of the objects, inaccordance with their positions either with the first sub-region or withthe second sub-region, to associate a track with each of the objects,wherein the track is determined from positions of the object in thesequence of images, wherein the track has a starting position locatedeither in the first sub-region or in the second sub-region, to associatea memory state with each of the objects on the basis of its trackwherein, with a given starting position of the track, the memory stateis dependent on whether the respective object is associated with thefirst sub-region or the second sub-region, wherein the memory state is anumber that, when the respective object transfers between the firstsub-region and the second sub-region, is incremented by a first value,wherein a first memory state is present if the number is an odd multipleof the first value, and wherein a second memory state is present if thenumber is an even multiple of the first value, and to take into accountmultiple transfers of the same object between the first sub-region andthe second sub-region when determining the number of transfer objects.8. The system according to claim 7, wherein the sensor arrangementcomprises an optical sensor selected from the group consisting of aphoto camera, a CCD camera, a stereo camera, a video camera, a streakcamera and a time-of flight camera.